Absorbent vegetable material and process for making same

ABSTRACT

An absorbent material derived from a vegetable material containing pectin.

This is a continuation of application Ser. No. 522,873, filed On Aug.11, 1983, now abandoned.

TECHNICAL FIELD

This invention relates to novel absorbent materials of vegetable origin,and the process for making such absorbent materials.

Disposable absorbent products (e.g. disposable diapers, sanitarynapkins, and the like) generally contain absorbent webs of wood pulpfibers. Depending on the climate, it takes a tree from about 20 years toabout 40 years to mature to a harvestable state. Consequently, to meetthe demand for wood pulp fibers to be used in absorbent materials, vastareas of land are necessary for the growing of trees. As anotherconsequence, even though wood pulp fibers are probably the mosteconomical material for use in disposable absorbent products availabletoday, substantial expenditures are being made in the harvesting andgrowing of the trees. There is therefore a continuing need foralternative, inexpensive absorbent materials, preferably from renewableresources.

It has now been discovered that certain pectin-containing agriculturalby-products can be converted to highly absorbent materials, suitable foruse in disposable absorbent products, via a relatively simple andinexpensive process. Typical examples of agricultural by-productssuitable as raw materials for the absorbent materials of the presentinvention include the residue material from citrus juice processors andfrom sugar beet refineries. These materials are therefore abundantlyavailable at low cost.

The pectin-containing agricultural residue material can be converted toa highly absorbent material by a process involving hydrolysis or partialhydrolysis of the pectin methyl esters present in waste materials; andsubsequent washing and drying of the material. The absorbent propertiesof the materials may be further improved by subject them to a bleachingstep. Such a bleaching step also improves the appearance of the product,thereby making it more acceptable for use in disposable absorbentproducts. The vegetable-derived absorbent materials typically have anabsorbent capacity which is from 2 to 5 times that of conventional woodpulp fiber webs. These materials therefore offer an opportunity toreduce the bulk of absorbent products while maintaining theircontainment capacity.

It is therefore an object of this invention to provide an inexpensiveabsorbent material, suitable for use in disposable absorbent products.It is another object of this invention to provide a process forconverting certain pectin-containing agricultural waste materials to theabsorbent materials of this invention.

BACKGROUND OF THE INVENTION

The agricultural waste materials suitable as starting materials for themanufacturing of the absorbent materials of the present invention arebeing produced in large quantities. The waste material from citrus juiceprocessors consisting of peels (i.e. albedo and flavedo) and rag, isgenerally processed to cattle feed by what has been termed the "limede-watering process". This process comprises the steps of treating thewaste with "lime" (calcium oxide, calcium hydroxide, or even calciumcarbonate) to convert it from a slimy, unpressable condition to awatery, pressable condition; pressing the converted waste; and drying(see, for example, U.S. Pat. No. 2,147,521, issued Feb. 14, 1939 toFlorida Citrus Exchange; U.S. Pat. No. 2,215,944, issued Sept. 24, 1943to Vincente, U.S. Pat. No. 2,362,014, issued Nov. 7, 1944 to CitrusProcesses, Inc.).

Relatively small quantities of citrus waste are used as a source ofpectin, which can be used as a thickening agent in food products. Foodthickening agents may also be prepared by comminuting citrus peelmaterial, and lowering the degree of esterification of the pecticmaterials in the citrus peel by enzymatic or chemical treatment. Thisapproach has been disclosed in U.S. Pat. No. 3,982,003 issued Sept. 21,1976 to Mitchell et al., and in U.S. Pat. No. 4,143,172, issued Mar. 6,1979 to Mitchell et al. Another attempt at converting citrus waste to afood additive for human consumption is disclosed in U.S. Pat. No.4,225,628, issued Sept. 30, 1980 to Lynn. According to the processdescribed in this reference, citrus peel particles are de-watered by aprocess very similar to the lime de-watering process used in cattle feedproduction; the material is subsequently mixed with sesame grain flour,ground, dried and milled to a desired particle size. U.S. Pat. No.4,379,782, issued Apr. 12, 1983 to Staub et al. discloses the use ofcitrus albedo or sugar beet pulp as a dietary fiber. The material isextracted with water or isopropanol to remove soluble carbohydrates andcolor and flavor materials. In spite of these attempts at finding moreprofitable uses for citrus waste, almost all of the citrus waste fromjuice canneries is still being converted in cattle feed and sold at aprice which barely provides for recovery of the processing costs.

Sugar beet residue (commonly referred to as beet pulp), like citrusresidue, is generally converted to cattle feed. As for citrus residues,attempts have been reported to convert beet pulp into a food additivesuitable for human consumption. An example is Japanese Patent SHO57-54573, publication date Apr. 1, 1982. This patent discloses a methodfor upgrading beet pulp by bleaching the pulp in hypochloric acid at pH6.5 to 7.5, washing with water and drying. The material is reported tobe capable of absorbing about 90% of its weight in water.

SUMMARY OF THE INVENTION

The present invention relates to vegetable absorbent materialcomprising: (a) from about 15% to about 80% pectin, having a degree ofesterification of from about 1% to about 45% and less than about 50% ofthe pectin being in the form of a salt of a divalent cation; (b) fromabout 15% to about 80% of a material selected from the group consistingof cellulose, hemicellulose, lignin, and mixtures thereof; (c) from 0%to about 1% chloroform soluble lipids; and (d) from 0% to about 10%non-lipid organic materials extractable in a mixture of chloroform,methanol and water, said mixture having a volume ratiochloroform:methanol: water of 20:4:1; and (e) and 0% to about 6%water-soluble metal salts.

This invention further relates to a process for preparing an absorbentmaterial from a pectin-containing vegetable material, comprising thesteps of: (a) comminuting the vegetable material to an average particlesize of from about 0.05 mm to about 3 mm; (b) de-esterifying the pectinto a degree of esterification of less than about 45%; (c) washing thevegetable material in soft water; and (d) drying the vegetable materialto a moisture content of less than 15%.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 represents a flow chart of the analytical protocol used incharacterizing the absorbent materials of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to novel vegetable absorbent materials, a processfor making the absorbent materials, and absorbent products comprisingthese novel absorbent materials.

This invention is based upon the discovery that pectin-containingvegetable materials can be converted into absorbent materials, using arelatively simple and inexpensive process. Pectin-containing vegetablematerials which are suitable as starting materials for the production ofthe absorbent materials of the present invention contain at least about15% pectin. Examples include apples, apricots, citrus peels, sugar beetsand watermelon rinds. Zucchini for example, which has a pectin contentof about 8%, is not suitable. Citrus peels and sugar beet pulp, each ofwhich is a by-product of an important agricultural industry, areavailable in large quantities and at low cost and are thereforepreferred starting materials for the preparation of the absorbentmaterials of the present invention.

The composition parameters of the vegetable starting materials and ofthe vegetable absorbent materials obtained upon processing have beendetermined in the comprehensive analytical protocol given below.Percentages of components of the materials, as used herein, are weightpercentages as determined by this analytical protocol, except"equivalent percent divalent metals" and "degree of esterification",which are equivalent percentages of the total amount of polygalacturonicacid. Data obtained by a different analytical method, however, maydiffer, which precludes a direct comparison with such data. Inparticular the pectin, cellulose and hemicellulose contents and thedegree of esterification which are determined indirectly, are parameterswhich are sensitive to the analytical method used.

In the analytical protocol the water content of a sample of the materialto be analyzed is determined by Karl Fischer titration. The amounts ofcalcium, magnesium, sodium and potassium are determined by dry ashingfollowed by flame atomic absorption analysis of these metals. A thirdsample of the material is subjected to water extraction followed by a40-hour Soxhlet extraction with chloroform. The amount of lipids in theextract is determined gravimetrically (hereinafter referred to as"chloroform soluble lipids"). If the material to be analyzed does notcontain components which are both water-soluble and chloroform-soluble,the water extraction prior to the chloroform extraction may be omitted.Thus, it has been found that a chloroform extract of citrus peel derivedabsorbent materials does not contain watersoluble components, but that asugar beet derived absorbent material does contain water-solublecomponents in the chloroform extract. A citrus peel-derived material maytherefore be extracted with chloroform without prior water extraction,and an accurate reading of the amount of chloroform soluble lipids isobtained; a sugar beet derived material, on the other hand, must beextracted with water prior to chloroform extraction in order to obtainan accurate determination of the amount of chloroform soluble lipids.

A fourth sample is extracted with chloroform, and is subsequentlysubjected to a 40 hour Soxhlet extraction with chloroform/methanol/water(20/4/1, v/v/v). (If the determination of chloroform soluble lipids wasmade without prior water extraction the residue of that test can be usedfor this chloroform/ methanol/water extraction.) The amount of extractedmaterial, which is determined gravimetrically, is the sum of the amountsof water-soluble metal salts and non-lipid organic materials. The metalcations are determined by flame ionization; the amount of water-solublemetal salts (hereinafter referred to as "watersoluble metal salts") iscalculated therefrom using the molecular weight of the prevalent anion(which is known from the processing history of the sample; in case ofchlorine bleaching, for example, the prevalent anion is chloride). Theamount of nonlipid organic materials (hereinafter referred to as"non-lipid organic materials") is determined by subtracting the amountof water-soluble metal salts from the total amount of material extractedwith the chloroform/methanol/water mixture.

The residue of the chloroform/methanol/water extraction containscellulose, hemicellulose, lignin, pectin and pectates. The residue issplit in four parts; one part is subjected to an acid hydrolysis ofcellulose and hemicellulose, followed by GC analysis of thealdonitrileperacetate derivatives of the sugars. The second part of theresidue is analyzed for protein; the protein content is calculated fromthe nitrogen value which is determined calorimetrically using theNessler reagent. The third part of the residue is analyzed for lignin,using the gravimetrical method TAPPI T222-os-74. The fourth part of theresidue is analyzed for calcium, magnesium, sodium and potassium by dryashing followed by flame atomic absorption analysis of the metals. Theamount of pectin is calculated from the total amount of bound metals(i.e., metals which cannot be removed by chloroform extraction orchloroform/methanol/water extraction) and the methoxy content. From theamounts of bound calcium and magnesium and the amount of pectin in thesample, the equivalent percent divalent metals is calculated as theequivalent percent of the polygalacturonic acid which is present asdivalent metal salt. Likewise, the degree of esterification iscalculated as the equivalent percent of the polygalacturonic acid whichis present as the methyl ester, from the methoxy content and the totalamount of pectin in the sample.

The analytical protocol is illustrated by the flow chart of FIG. 1. Thewater content 1 is determined by Karl Fischer titration. The methoxycontent 2 is determined by base hydrolysis followed by GC analysis ofthe liberated methanol. Total metals 3 are determined by dry ashingfollowed by flame atomic absorption analysis of the metals. Lipids 4 aredetermined by gravimetry after a 40-hour Soxhlet extraction withchloroform. The residue of the chloroform extraction is then subjectedto a 48-hour Soxhlet extraction with chloroform/methanol/water (20/4/1,v/v/v), other extractables 5 are determined gravimetrically. Lignin 6 isdetermined by gravimetry using TAPPI method T222-os-74. Protein 7 iscalculated from the nitrogen value which is determined colorimetricallyusing the Nessler reagent. Cellulose and hemicellulose 8 are determinedby acid hydrolysis followed by GC analysis of thealdononitrileperacetate derivatives of the sugars. Bound metals 12 aredetermined by dry ashing followed by flame atomic absorption analysis ofthe metals. Pectin 9 is calculated from the sum of the methoxy content 2and bound metals 12. From bound calcium 12 and pectin 9 is calculatedthe equivalent percent calcium 11. From methoxy content 2 and pectin 9is calculated the degree of esterification 10 as equivalent percent ofpolygalacturonic acid which is present as the methyl ester.

"Pectin", as determined by this method is the material in thecomposition which is capable of forming methyl esters or binding metals,calculated as polygalacturonic acid. The underlying assumptions are thatthe pectin does not contain any free acid groups, that all of the pectinis anhydrogalaturonic acid, and that no insoluble alkaline earth metalsalts, other than calcium salts, are present. These assumptions havebeen verified by independent methods to be correct within a reasonablemargin of confidence.

The sum of cellulose and hemicellulose is taken to be the total ofneutral sugars left in the sample after the extractions with chloroformand the chloroform/methanol/water mixture. Cellulose may be determinedseparately as the total amount of glucose. The balance of neutral sugarsis hemicellulose.

It has been discovered that the pectin in the composition plays animportant part in determining the absorbent properties of the material.Although compositions differ among species and within species, more than60% of the pectin in vegetable materials is generally present in theform of the methyl ester. In the case of organ peels, on the order of20% is present as the calcium salt; the balance is generally in theprotonated form, or an alkali metal salt, mostly potassium. The pectinin the absorbent materials of the present invention has a degree ofesterification of less than about 45%. The vegetable starting materialmust therefore be subjected to a deesterification step which may becarried out by alkaline treatment of a pH of from about 8 to about 13,or by an enzyme such as pectin-esterase. The enzyme is naturally presentin citrus peel.

Care should be taken that the amount of divalent metal pectates is notsubstantially increased. In particular, calcium pectates have been foundto be detrimental to the absorption properties of the material.Moreover, the calcium pectates once formed cannot be readily convertedto other pectic materials like alkali metal salts or pectic acids. Ingeneral, the total equivalent * of divalent metals must be less than50%. The equivalent % of calcium is preferably less than 30%. Inpractical terms this means that calcium hydroxide or calcium carbonatecannot be used for alkaline deesterification. It is not necessary,however, to use distilled or deionized water: tap water has been foundto not significantly reduce the absorbent properties of the materials,provided the water hardness does not exceed about 7 grains/gallon(corresponding to about 120 ppm CaCO₃) and provided that no excessiveamounts of water are used. The term "soft water" as used hereintherefore refers to water having a degree of hardness of less than 7grains/gallon (less than about 120 ppm CaCO₃).

In particular when citrus waste is used, the vegetable starting materialmay contain complex mixtures of lipids and lipid-like materials, andother non-polymeric organic materials. The absorbent properties of theresulting absorbent material may be greatly enhanced by removing theseorganic extractable materials. It has been discovered that the organicextractables generally belong to one of two classes; a first class ofmaterials which are soluble in chloroform and which have been identifiedas mostly non-polar lipids (these materials are referred to herein as"chloroform soluble lipids"); and a second class of materials which arenot soluble in chloroform alone, but which are soluble in a mixture ofchloroform, methanol and water (chloroform: methanol: water =20:3:1(v/v/v)). This second class of materials is comprised of non-lipidorganic materials and of water-soluble metal salts. The absorbentmaterials of the present invention may not contain more than about 1%chloroform soluble lipids, not more than about 10% non-lipid organicmaterials, and not more than about 6% water-soluble metal salts.

Hence, the present invention relates to vegetable absorbent materialscomprising (a) from about 15% to about 60% pectin, said pectin having adegree of esterification of from about 1% to about 45%, and less thanabout 50% of the pectin being in the form of a divalent metal salt; (b)from about 15% to about 80% of a material selected from the groupconsisting of cellulose, hemicellulose, lignin and mixtures thereof; (c)from 0% to about 1% chloroform soluble lipids; (d) from 0% to about 10%non-lipid organic materials extractable in a mixture of chloroform,methanol and water, said mixture having a volume ratiochloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.

Although the degree of esterification of the pectin does not appear tohave a major effect on the ultimate absorption capacity of the absorbentmaterial, low degrees of esterification are conducive to good wickingproperties of the material. High wicking rates are important for a fastuptake of liquid. For use in absorbent products like disposable diapers,sanitary napkins and the like, good wicking properties of the absorbentmaterial are highly desirable. The absorbent materials therefore mustcontain pectin which has a degree of esterification of less than about45%, preferably less than about 20%.

The second major component of the absorbent material, next to pectin, isgenerally a mixture of cellulose, hemicellulose and lignin. The actualcomposition of this mixture is to a large extent determined by thechoice of the raw material, and to a lesser extent by the process. Forexample, hemicellulose is likely to be partially removed duringprocessing, which increases the relative amounts of cellulose and ligninin the mixture. Depending on the raw material source, the amount oflignin may be very small. For example, citrus waste has a much lowerlignin level than beet pulp; yet very good absorbent materials can beprepared from either starting material.

It has been discovered that divalent metal pectates, in particularcalcium pectates, are far inferior to alkali metal pectates (e.g. sodiumpectates) with regard to absorbent properties. This is probably due tothe fact that divalent metal salts of pectin are "cross-linked", wherebythe divalent metal ion serves as the link between two adjacent pectinmolecules. This crosslinking is believed to prevent swelling of thepectin and to thereby reduce its absorbency. Some of the pectin isnaturally present as the calcium salt. Care must be taken not toincrease the amount of calcium pectate any further. Therefore, duringprocessing the materials should not be exposed to excessive amounts ofcalcium. If calcium is present in the form of an insoluble mineral saltwhich is not capable of interacting with the esterified pectin, thepresence of calcium is probably not harmful at all.

One specific embodiment of this invention is a citrus peelderivedabsorbent material comprising: (a) from about 30% to about 60% pectin,said pectin having a degree of esterification of less than about 20%,and less than about 30% of the pectin being in the form of a divalentmetal salt; (b) from about 30% to about 60% of a mixture of celluloseand hemicellulose; (c) from 0% to about 1% chloroform soluble lipids;(d) from 0% to about 10% non-lipid organic materials extractable in amixture of chloroform, methanol and water, said mixture having a volumeratio chloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts. Preferably, the peels of the ripe oranges orgrapefruits are used as a starting material and the process is carriedout in a way as to avoid excessive removal of hemicellulose.

A second specific embodiment of this invention is a sugar beet-derivedabsorbent material comprising: (a) from about 15% to about 35% pectin,said pectin having a degree of esterification of less than about 45%(preferably less than about 20%), and less than about 30% of the pectinbeing in the form of a divalent metal salt; (b) from about 20% to about80% of a mixture of cellulose and hemicellulose; (c) from 0% to about 1%chloroform soluble lipids; (d) from 05 to about 10% non-lipid organicmaterials extractable in a mixture of chloroform, methanol and water,said mixture having a volume ratio chloroform:methanol:water of 20:4:1;and (3) from 0% to about 6% water-soluble metal salts.

Process

The process for preparing the vegetable absorbent material from thepectin-containing starting material depends to a large extent on thestarting material being used. The process is aimed at reducing thedegree of esterification of the pectin in the material, and removingexcessive amounts of extractable materials. The process thereforecomprises the steps of (1) comminuting a pectin-containing vegetablematerial to a particle size of from about 0.05 mm to about 3 mm; (b)de-esterifying the pectin to a degree of esterification of less thanabout 45%; (c) washing the vegetable material in soft water; and (d)drying the vegetable material to a moisture content of less than 15%.

The manner in which the deesterification is carried out is not criticaland may, for example, be enzymatic or chemical.

Chemical deesterification of pectin may be carried out at acid oralkaline pH. Acid deesterification is not preferred as it is slow andleads to both divalent ion extraction and hemicellulose degradation.Alkaline deesterification is preferred but care must be exercised.Pectin methyl ester can degrade via a beta-elimination mechanism, so pHand temperature should be carefully controlled. Enzymaticdeesterification may be carried out with the enzyme pectinesterase; thisis particularly convenient when citrus peels are used as startingmaterial because the enzyme pectinesterase is naturally present incitrus peels. Alternatively, deesterification may be carried out bysoaking the vegetable material particles in a solution of an alkalimetal hydroxide. The reaction rate increases with the concentration ofhydroxyl ions, therefore the higher the pH, the faster the reaction willbe. The pH should therefore be above about 8, preferably above about 9.Excessively high pH values tend to result in removal of hemicelluloseand other desirable materials. Therefore, the pH should not exceed about13, and preferably be below about 12. A degree of esterification of lessthan 45% is generally achieved after about 2 minutes at pH 9.5 orgreater. As beta-elimination is very temperature dependent, atemperature of about 25° C. or lower is preferred. Prolonged contactingof the vegetable material with the alkali hydroxide solution results ina progressively lower degree of esterification of the pectin. It isgenerally not necessary to continue this deesterification step for morethan about 2 hours, since little additional benefit is obtained by doingso.

The washing of the material is critical, since it is necessary to removethe alkaline material and excess soluble materials. Washing may be donewith water or with an organic solvent. The latter has the advantage thatchloroform-soluble lipids which may be present in the material aregenerally to some extent removed by an organic solvent like acetone, butnot by a water wash. The washing step may be conveniently carried out asfollows. Excess liquid is drained off from the reaction mixture of thedeesterification step. Then, enough of the washing liquid (i.e. water oran organic solvent) is added in order to obtain a slurry with a solidscontent of about 2%. The slurry is equilibrated for about 5 to 15minutes, and then the washing liquid is drained off. This washing stepmay be repeated. The number of washing steps is determined by the amountof contaminants in the starting material and the desired composition ofthe finished absorbent material. Typically, 2 or 3 washing steps will benecessary.

After excess washing liquid has been drained off after the last washingstep, the liquid content of the remaining material is on the order ofabout 90%. This must be reduced to less than about 20% in order toobtain an absorbent material with optimum absorption properties. If anorganic solvent is used in the washing step (e.g. acetone, isopropylalcohol, or methanol), this solvent may be simply removed by evaporatingit. The material may also be dried by solvent displacement: after thelast washing step with water, the material is slurried up with anorganic solvent like acetone or methanol, the solvent is then drainedoff and the excess is evaporated.

For economical reasons it may not be feasible to use any organicsolvents in the process. In that case, water will have to be removedusing a conventional drying technique. This may be either freeze drying,vacuum drying, or thermal drying. Of these three, freeze drying is themost attractive because it does not cause collapse of the finecapillaries which are naturally present in the material. Unfortunately,freeze drying is also the most expensive drying method of these three.

Thermal drying is economically the most attractive method of dryingavailable. If the 90% moisture product from the washing step is dried inan oven, a board-like material is obtained which is not very absorbent.It has been discovered, however, that the material may be dried byspraying it into a counter current of superheated steam or heated air.The inlet temperature and the flow rate should be controlled as toresult in an outlet temperature in the range of from about 60° C. toabout 75° C. This results in a product which has a moisture content ofless than 15%. Although thermally dried materials possess goodabsorption capacities, the absorption kinetics of such materials tend tobe slow. The rate of absorption can be vastly improved by adding asurfactant to the slurry during the last washing step. An amount ofsurfactant of from about 1% to about 3% by weight of the amount of theslurry is generally sufficient. The type of surfactant is not critical.Examples of suitable surfactants are nonionic surfactants, e.g.ethoxylated fatty alcohols.

It is highly desirable to include in the process a bleaching step.Preferably, the bleaching is carried out with an oxidative bleachingagent. Examples of suitable bleaching agents are hydrogen peroxide,perborate, hypochlorite, chlorine dioxide and chlorine. Sodiumhypochlorite is a preferred bleaching agent. For optimum properties ofthe absorbent material, and optimum safety of absorbent products madetherewith, excess bleach and electrolytes introduced during thebleaching step will have to be removed. Bleaching is therefore bestcarried out prior to the washing steps. Since color compounds may beformed during alkaline deesterification, the bleaching step is bestcarried out subsequent to the deesterification step if alkalinedeesterification is used (as opposed to enzymatic deesterification). Inorder to improve the effective use of the bleaching agent, it isdesirable to include a washing step subsequent to the deesterificationstep and prior to the bleaching step, especially when citrus peels arethe starting material. Hence, in case alkaline deesterification andbleaching are used, the process sequence is as follows: (a) communitingthe pectin-containing vegetable material to a particle size of fromabout 0.05 mm to about 3 mm; (b) soaking the pectin-containing vegetablematerial particles obtained in step (a) in a solution of an alkali metalhydroxide in water at pH of from about 9 to about 12 and at atemperature of from about 15° C. to about 50° C., for a period of fromabout 2 minutes to about 120 minutes; (c) washing the product of step(b) in soft water; (d) bleaching the product of step (c) for from about5 minutes to about 60 minutes; (e) washing the product of step (d) insoft water; and (f) drying the product of step (e).

The effect of bleaching is two fold. It removes color materials, therebyvastly improving the appearance of the absorbent material obtained bythis process, and making it more suitable for use in consumer productslike disposable diapers, sanitary napkins and the like. Bleachingfurther tends to decompose chloroform-soluble lipids into water-solublefragments. Consequently, the bleaching step significantly reduces thelevel of chloroformsoluble materials in the finished product.

The removal of chloroform-soluble lipids is particularly important whencitrus peels are used as the starting material. Citrus peels containhigh levels of such chloroform-soluble lipids, and if water (as opposedto organic solvents) is used in the washing steps of the process,bleaching is instrumental in reducing the level of chloroform-solublelipids to the desired level.

Although whole citrus peels may be used as the starting material, theflavedo part greatly increases the load of chloroform-soluble lipids andcolored materials. It is therefore desirable to remove the flavedo partof the peel. The flavedo may be shaved off mechanically by machinerywhich is commercially available and designed for this purpose. Suchequipment typically leaves about 30% of the flavedo on the albedo. Ithas been discovered that when these machine shaved peels are subjectedto the process described hereinabove (including the bleaching step) anabsorbent material is obtained which is negligibly less absorbent thanthe material obtained from an (handmade) all albedo starting material.Whole citrus peels may also be used as starting material. Highlyacceptable absorbent materials may be made therefrom, albeit at theexpense of a higher usage of bleaching chemicals.

Sugar beets, by their nature, contain only low levels ofchloroform-soluble lipids. When processing sugar beet pulp, one maytherefore forego the bleaching step is absorbent properties are the onlyconcern. However, during alkaline deesterification, beet pulp develops apersistent green color and a bleaching step may be highly desirable oreven necessary from an aesthetics viewpoint.

The processing of other pectin-containing raw materials will have becomeapparent from the foregoing. The bleaching step may be foregone if thestarting material has a low chloroformsoluble lipid content, andcontains little colored materials or if the aesthetics of the absorbentmaterial are relatively unimportant (e.g. when intended for industrialuse). The choice of the method of deesterification (enzymatic oralkaline treatment) is largely determined by economic determinations:enzymatic deesterification is relatively slow: alkaline treatment isfaster and lends itself better to a continuous operation of the process.The choice of the washing liquid (water or an organic solvent) islikewise determined by economic considerations with which a personskilled in chemical engineering may be deemed well familiar.

Performance Testing

A. Partition Test

Samples of absorbent materials were subjected to a partitioning test,more fully described hereinbelow. This test has been designed to measurethe absorption performance of the absorbent materials in competitionwith conventional cellulose fibrous webs, both under conditions of lowliquid load and high liquid loads. The absorption fluid was "syntheticurine" (a solution of 1% NaCl, 0.06% MgCl₂.6H₂ O and 0.03% CaCl₂.2H₂ Oin distilled water; the surface tension of the solution was adjusted to45 dynes/cm with about 0.0025% of an octylphenoxy polyethoxy ethanolsurfactant (Triton X-100, from Rohm and Haas Co.)). This test has beenfound to be predictive of the absorption capacity under typical usageconditions of absorbent materials when used as absorbent cores indiapers.

The partitioning tests were carried out as follows. A piece ofpolyethylene sheet (the kind of material generally used as a backsheetin disposable diapers) was placed on a flat, nonabsorbent surface. Around sample (57 mm diameter) of the absorbent material to be tested wasplaced on top of this backsheet. On top of that was placed a piece ofpaper tissue of the type generally used as envelope tissue in disposablediapers. On top of the envelope tissue was placed a sample of thereference material (southern soft wood slash pine fibrous web, 0.1 g/cm³density). Both sample and reference were prepared to have a weight asclosely as possible approaching 0.6 g, corresponding to a basis weightof about 0.02 g/cm². The top sample was wetted with a predeterminedamount (about 1 g) of synthetic urine, covered with another piece ofbacksheet, upon which a weight of 4.4 pounds (about 2 kg) was placed.This weight exerts a confining pressure of 1 psi (about 7×10³ N/m²)(when confined the samples have a diameter of about 60 mm). After fiveminutes equilibration time, the weight was removed and the two samplesof absorbent material were weighed separately. To facilitate removal, aplastic mesh screen was placed in between the samples prior to the test.The "X-load", defined as the amount of synthetic urine (in grams)absorbed per gram of absorbent material was calculated for each sample.The sample was then placed back under the confining weight, and dosedwith an additional dose of synthetic urine, equilibrated, and weighed.This was repeated several times (typically in the order of 8-10 times)so that the relative absorption performance of the test material over awide range of X-loads was obtained as a function of the loading in thereference top layer.

B. Capillary Sorption Test

The absorption properties of absorbent materials were determined bytheir "synthetic urine" absorption and desorption behavior. The basicprocedure and the design of the apparatus are described by Burgeni andKapur, "Capillary Sorption Equilibria in Fiber Masses", Textile ResearchJournal, 37 (1967) 362, which publication is incorporated herein byreference. The test is particularly useful for determining absorptionkinetics.

The absorption apparatus consisted of a horizontal capillary tube,approximately 120 cm long, connected by a valve to a fluid reservoir.The end of the tube was connected by tygon tubing to a glass funnelcontaining as ASTM 4-8 micron frit on which the absorbent materialsample was placed under a confining pressure of 1 psi (about 7×10³N/m²). The glass frit funnel was mounted on a vertical pole. The heightof the frit above the capillary tube determined the hydrostatic suctionbeing exerted on the sample. In a typical absorption/desorptionexperiment the volume of absorbed synthetic urine was determined as afunction of hydrostatic suction, starting at 100 cm.

A simplified test was developed to determine the useful capacity of anabsorbent web. In this test, the absorbed volume at -25 cm hydrostaticpressure was measured ("25 cm, Absorption"). Next, the frit containingthe sample was lowered to zero hydrostatic pressure and the equilibriumvalue of sorbed volume measured ("0 cm, Void Volume"). Then the frit wasraised again to the 25 cm mark and the absorbed volume at -25 cm in thedesorption mode was determined ("25 cm, Desorption"). Readings of 25 cmabsorption and 25 cm Desorption volumes were made after an equilibriumtime of 20 minutes; readings of 0 cm Void Volumes were done after anequilibration time of 30 minutes.

Example One

Florida Valencia oranges juiced with an AMC Extractor were hand shavedto remove the flavedo and rag. The albedo was ground in an UrschelGrinder. Twenty-three pounds (about 10 kg) of the ground raw material,at 11.96% solids, was slurried in 75 pounds of water (about 34 kg),making a 2.8% solids slurry. The slurry was titrated to pH 9.5 andmaintained at this pH by caustic addition for 30 minutes. The titrationtook 1.25 liters of 1N sodium hydroxide. The material was dewatered in abasket centrifuge. It was washed with 75 pounds (about 34 kg) of waterwhile spinning in the centrifuge, and dewatered again. The 14.7 pounds(6.7 kg) of filter cake at 10.715 solids that resulted from this wasslurried in 43 pounds (19.5 kg) of water, making 2.8% solids slurry. 3.8liters of 5.15% sodium hypochlorite solution were added to the slurryand mixed for 15 minutes. The bleached material was dewatered in thecentrifuge. It was washed again with 75 pounds (about 34 kg) of waterwhile spinning and then dewatered. This resulted in 12.2 pounds (5.5 kg)of material at 10.3% solids for a yield of 45.7%.

The material was freeze-dried to a moisture content of about 10%. Thechemical composition was determined by the analytical method describedhereinabove. The absorption properties were determined by the CapillarySorption and Partition tests described hereinabove, and compared tothose of conventional wood pulp fiber webs.

    ______________________________________                                        A. GROSS CHEMICAL COMPOSITION                                                 Component      Coposition (% of dry weight)                                   ______________________________________                                        Pectin         44.0                                                           Other polymers 52.7                                                           Chloroform soluble lipids                                                                    0.70                                                           Non-lipid organics                                                                           2.49                                                           Water-soluble metal salts                                                                    0.13                                                           ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                          Component     Equivalent % polygalacturonic acid                              ______________________________________                                        Methyl ester  14.4                                                            Divalent metal salts                                                                        29.8                                                            Monovalent metal salts                                                                      55.8                                                            ______________________________________                                        C. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               Reference  Citrus Absorbent                                   Test Conditions Wood Pulp  Material                                           ______________________________________                                        25 cm Absorb, 20 min                                                                          1.9        8.4                                                0 cm Void Volume, 30 min                                                                      4.5        9.4                                                25 cm Desorb, 20 min                                                                          3.8        8.5                                                ______________________________________                                        D. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Citrus Absorbent                                                 Wood Pulp    Material                                                         ______________________________________                                        0.8          3.6                                                              1.0          5.5                                                              1.5          7.1                                                              2.4          8.1                                                              3.7          8.7                                                              4.9          9.7                                                              ______________________________________                                    

As the data indicate, a highly absorbent material was obtained. Theabsorbent properties of this material were far superior to those of aconventional wood pulp fiber web.

A second bath of citrus peel absorbent material is prepared by the samemethod. This batch is dried in a flash dry process, as follows. Thefilter cake obtained after the last centrifuge dewatering step is mixedin a 1% surfactant solution (Tergitol 15-S-9) to a 2.5% solids slurry.The slurry is mixed for 15 minutes. The material is dewatered in abasket centrifuge. The resulting filter cake is flash dried in twopasses. On the first pass, the air inlet temperature is maintainedbetween 150° C. and 200° C., and the air-flow is maintained so as toresult in an outlet temperature between 60° C. and 65° C. On the secondpass the inlet temperature is maintained between 90° C. and 125° C., andthe outlet temperature between 50° C. and 55° C. A highly absorbentmaterial is obtained.

Example Two

Four hundred thirty-four grams of finely ground sugar beet cattlefeed at16.38% solids were slurried in 3 liters of water, making a 2.1% solidsslurry. The slurry was titrated to pH 9.5 and maintained by causticaddition for 30 minutes. The titration took 12 ml of 1N sodiumhydroxide. The material was dewatered in a basket centrifuge. It waswashed with 50 pounds (22.7 kg) of water while spinning in thecentrifuge, and then dewatered. The 462 grams of filter cake at 12.03%solids that resulted from this was slurried in 3 liters of water, makinga 1.6% solids slurry. Five hundred ml of 5.25% sodium hypochlorite wasadded to this and it was mixed for 17 minutes. The bleached material wasdewatered in the centrifuge. It was washed again with 50 pounds (22.7kg) of water while spinning, and then dewatered. This resulted in 496grams of material at 11.2% solids for a yield of 78%.

The material was freeze-dried to a moisture content of about 10%. Thechemical composition was determined by the analytical method describedhereinabove. The absorbent properties were determined by the CapillarySorption and Partition Tests described hereinabove.

    ______________________________________                                        A. GROSS CHEMICAL COMPOSITION                                                 Component      Composition (% of dry weight)                                  ______________________________________                                        Pectin         15.5                                                           Other polymers 76.1                                                           Chloroform soluble lipids                                                                    0.40                                                           Non-lipid organics                                                                           6.79                                                           Water soluble metal salts                                                                    1.60                                                           ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                          Component     Equivalent % polygalacturonic acid                              ______________________________________                                        Methyl ester  22.9                                                            Divalent metal salts                                                                        25.4                                                            Monovalent metal salts                                                                      51.7                                                            ______________________________________                                        C. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Sugar Beet Absorbent                                             Wood Pulp    Material                                                         ______________________________________                                        1.0          3.5                                                              2.0          5.3                                                              3.0          6.9                                                              4.0          8.3                                                              5.0          10.0                                                             ______________________________________                                        D. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               Reference Sugar Beet Absorbent                                Test Conditions Wood Pulp Material                                            ______________________________________                                        15 cm Absorb, 20 min                                                                          1.9       6.3                                                 0 cm Void Volume, 30 min                                                                      4.5       7.9                                                 25 cm Desorb, 20 min                                                                          3.8       6.5                                                 ______________________________________                                    

The data demonstrate that the material is highly absorbent.

Example Three

Five hundred grams of soaked, finely ground cattle feed (as used in theabove Example Two) at 16.3% solids was mixed with 1.5 liters of a 5.2%solution of sodium hypochlorite (CLOROX, from Clorox Co., Oakland, CA)and 1.5 liters of distilled water and agitated for 15 minutes. It wasdeliquored in a basket centrifuge and washed with 30 liters of distilledwater.

The material was freeze-dried to a moisture content of about 10%. Thechemical composition was determined by the analytical method describedhereinabove. The absorbent properties were determined by the CapillarySorption and Partition Tests described hereinabove.

    ______________________________________                                        A. GROSS CHEMICAL COMPOSITION                                                 Component      Composition (% of dry weight)                                  ______________________________________                                        Pectin         31.2                                                           Other polymers 57.7                                                           Chloroform soluble lipids                                                                    0.40                                                           Non-lipid organics                                                                           10.3                                                           Water soluble metal salts                                                                    0.85                                                           ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                          Component     Equivalent % polygalacturonic acid                              ______________________________________                                        Methyl ester  35.4                                                            Divalent metal salts                                                                        18.4                                                            Monovalent metal salts                                                                      46.2                                                            ______________________________________                                        C. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Sugar Beet Absorbent                                             Wood Pulp    Material                                                         ______________________________________                                        0.9          1.1                                                              1.0          2.8                                                              1.3          4.6                                                              1.8          5.7                                                              2.9          6.5                                                              3.5          7.5                                                              4.2          8.7                                                              ______________________________________                                        D. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               Reference Sugar Beet Absorbent                                Test Conditions Wood Pulp Material                                            ______________________________________                                        25 cm Absorb, 20 min                                                                          1.9       6.2                                                 0 cm Void Volume, 30 min                                                                      4.5       7.2                                                 25 cm Desorb, 20 min                                                                          3.8       6.1                                                 ______________________________________                                    

The data demonstrate that the material is highly absorbent.

Example Four

Two pounds (9.9 kg) of sugar beet cattle feed was soaked in 3 gallons(11 liters) of distilled water overnight at room temperature. The soakedfeed was then coarsely chopped in a Waring blender and finely ground inan Urschel grinder. Enough distilled water was added to make a 1.5%solids slurry. To this slurry was added 300 ml of 1N NaOH over thirtyminutes to maintain the slurry pH at 9.5. The material was then washedin a basket centrifuge while spinning with 24 gallons (91 liters) ofdistilled water. The washed cake was mixed with 5 gallons (19 liters) ofa 5.2% solution of sodium hypochlorite (CLOROX, from Clorox Co.,Oakland, CA) and 5 gallons (19 liters) of distilled water and mixed for15 minutes. The bleached material was deliquored in the basketcentrifuge for one minute and then washed with 3 gallons (11 liters) ofdistilled water while the centrifuge was still spinning. The washed cakewas slurried in 3 gallons (11 liters) of distilled water and deliquoredin the centrifuge. This procedure was repeated twice.

The material was freeze-dried to a moisture content of about 10%. Thechemical composition was determined by the analytical method describedhereinabove. The absorbent properties were determined by the CapillarySorption and Partition Tests described hereinabove.

    ______________________________________                                         A. GROSS CHEMICAL COMPOSITION                                                Component      Composition (% of dry weight)                                  ______________________________________                                        Pectin         24.7                                                           Other polymers 66.0                                                           Chloroform soluble lipids                                                                    0.40                                                           Non-lipid organics                                                                           8.10                                                           Water soluble metal salts                                                                    1.17                                                           ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                          Component     Equivalent % polygalacturonic acid                              ______________________________________                                        Methyl ester  16.9                                                            Divalent metal salts                                                                        31.1                                                            Monovalent metal salts                                                                      52.0                                                            ______________________________________                                        C. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Sugar Beet Absorbent                                             Wood Pulp    Material                                                         ______________________________________                                        0.9          1.0                                                              1.2          2.7                                                              1.7          4.4                                                              2.3          5.5                                                              3.4          6.3                                                              4.4          7.3                                                              4.6          8.3                                                              ______________________________________                                        D. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               Reference Sugar Beet Absorbent                                Test Conditions Wood Pulp Material                                            ______________________________________                                        25 cm Absorb, 20 min                                                                          1.9       6.0                                                 0 cm Void Volume, 30 min                                                                      4.5       6.6                                                 25 cm Desorb, 20 min                                                                          3.8       6.2                                                 ______________________________________                                    

The data demonstrate that the material is highly absorbent.

Example Five

A bath of Navel oranges were cut in half; the juice was extracted with ahome juicer. The flavedo was removed using a Brown peel shaver. About1200 grams of albedo was obtained, with some rag attached. The solidscontent of the sample was 11.5%.

The sample was mixed with 3.0 liters of distilled water in a largeWaring Blender at the highest speed for two minutes. The mixture wasallowed to stand for two hours, then dewatered over a Buchner funnel andwashed with 6 liters of distilled water. The wet mass was put into alarge container, and 3.8 liters of a 5.2% solution of sodiumhypochlorite (CLOROX, from Clorox, Co., Oakland, CA) were added. Themixture was stirred rapidly for one hour at ambient temperature, thendewatered, and washed three times over a Buchner funnel. This yielded amass of 590 g having a solids content of 7.5%. The material wasfreeze-dried.

Absorbency of the freeze dried material was measured using the CapillarySorption Test described hereinabove with distilled water and withsynthetic urine. Absorbency was also measured with the Partition Testdescribed hereinabove.

    ______________________________________                                                      Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               Reference  Citrus Absorbent                                   Test Conditions Wood Pulp  Material                                           ______________________________________                                        25 cm Absorb, 20 min                                                                          1.9        6.0                                                0 cm Void Volume, 30 min                                                                      4.5        7.6                                                25 cm Desorb, 20 min                                                                          3.8        7.0                                                ______________________________________                                                      Capacity, ml Distilled Water/g                                                Material, 1.0 psi                                                               Reference  Citrus Absorbent                                   Test Conditions Wood Pulp  Material                                           ______________________________________                                        25 cm Absorb, 20 min                                                                          2.8        5.8                                                0 cm Void Volume, 30 min                                                                      4.8        13.8                                               25 cm Desorb, 20 min                                                                          3.6        12.1                                               ______________________________________                                        B. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Citrus Absorbent                                                 Wood Pulp    Material                                                         ______________________________________                                        1.0          3.3                                                              2.0          5.5                                                              3.0          6.4                                                              4.0          7.2                                                              5.0          8.1                                                              ______________________________________                                    

Example Six Hydrolysis Time Variations

Florida Valencia oranges juiced with an AMC extractor were machineshaved in a Brown peel shaver to remove approximately 70% of the flavedoand 90% of the rag. The shaved peels were ground in an Urschel grinderto a particle size of approximately 0.6 mm. Approximately 195 pounds(88.5 kg) of the Urschel ground peel at 12.2% solids were slurried in380 pounds (172.5 kg) of distilled water making a 4.3% solids slurry. Atthis point a small batch was removed. This was the 0 minute exposurebath. While constantly agitating, the slurry was titrated to pH 9.8 andmaintained at this pH by caustic addition. Small batches were removed at30 and 120 minutes exposure time. Six normal hydrochloric acid was addedto bring each caustic treated batch to pH 7. All three batches weredewatered in a basket centrifuge, washed and dewatered again. They werewashed while spinning in a centrifuge with approximately 75 pounds (34kg) of distilled water per 17 pounds (7.7 kg) of washed, dewateredfilter cake. The filter cakes were added to enough 2.63% sodiumhypochlorite bleach solution to make a 2.5% solids slurry. The slurrieswere agitated 18 minutes. The bleached materials were dewatered in abasket centrifuge, washed, and dewatered again. They were washed whilespinning in the centrifuge with approximately 75 pounds (34 kg) ofdistilled water per 12 pounds (5.4 kg) of washed, dewatered filter cake.The bleached, washed materials were freeze dried to a moisture contentof approximately 10%. The chemical composition was determined by theanalytical method described hereinabove.

    ______________________________________                                        A. GROSS CHEMICAL COMPOSITION                                                               Composition (% of dry weight)                                                   Whole Peel                                                                    Starting  0       30   120                                    Component       Material  min     min  min                                    ______________________________________                                        Pectin          34.9      43.3    44.1 43.4                                   Other polymers  34.3      27.9    44.3 45.2                                   Chloroform soluble lipids                                                                     4.88      1.60    0.78 0.80                                   Non-lipid organics                                                                            25.0      17.7    6.81 6.99                                   Water-soluble metal salts                                                                     0.88      9.46    3.99 3.61                                   ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                                       Equivalent % polygalacturonic acid                                              Whole Peel                                                                    Starting   0       30    120                                   Component      Material   min     min   min                                   ______________________________________                                        Methyl ester   59.8       50.7    17.7  5.3                                   Divalent metal salts                                                                         30.4       19.2    25.6  28.6                                  Monovalent metal salts                                                                       9.8        30.1    56.7  66.1                                  ______________________________________                                        C. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                                               0         30        120                                       Test Conditions min       min       min                                       ______________________________________                                        25 cm Absorb, 20 min                                                                          5.1       6.2       6.8                                       0 cm Void Volume, 30 min                                                                      6.0       7.4       7.7                                       25 cm Desorb, 20 min                                                                          5.2       6.7       6.9                                       ______________________________________                                        D. CAPILLARY SORPTION RATE                                                               25 cm Absorption                                                              Rate, ml Synthetic Urine/g Material per                                       minute, 1.0 psi                                                                 0          30        120                                         Measurement Time                                                                           min        min       min                                         ______________________________________                                        15 sec       1.4        1.7       3.1                                         30 sec       2.2        2.9       5.2                                         45 sec       2.8        4.0       6.0                                         1 min        3.5        4.6       6.3                                         2 min        5.0        5.6       6.6                                         10 min       5.2        6.2       6.7                                         ______________________________________                                        E. PARTITION TEST                                                             Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference   Citrus Absorbent Material                                         Wood Pulp   0 Minute Sample                                                   ______________________________________                                        1.1         1.1                                                               1.5         2.7                                                               2.3         4.2                                                               3.8         4.8                                                               4.8         5.9                                                               ______________________________________                                        Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference   Citrus Absorbent Material                                         Wood Pulp   30 Minute Sample                                                  ______________________________________                                        0.9         1.3                                                               1.1         3.2                                                               1.4         5.0                                                               2.0         6.4                                                               3.3         7.2                                                               4.3         8.0                                                               ______________________________________                                        Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference   Citrus Absorbent Material                                         Wood Pulp   120 Minute Sample                                                 ______________________________________                                        0.9         1.2                                                               1.0         3.4                                                               1.2         5.0                                                               2.0         6.4                                                               3.3         7.3                                                               4.4         8.0                                                               ______________________________________                                    

The absorption properties were determined by the Capillary Sorption andPartition Tests described hereinabove.

The starting material (machine shaved orange peel) exceeded the limitsset for chloroform soluble lipids, non-lipid organics and degree ofesterification for absorbent materials of the present invention. The 0min. sample, which is different from the starting material in that ithas been bleached and washed, had a chloroform soluble lipids contentwithin limits, probably due to the bleaching step. Hydrolysis withsodium hydroxide further improved the chemical composition of thematerial, resulting in a corresponding increase of the absorbentcapacities. A low degree of esterification increased the sorption rateof the sample.

Example Seven

One batch of orange peels was converted to absorbent material, using thewhole peel (i.e., no flavedo was shaved off), using the method describedin Example Seven (hydrolysis time: 30 min., bleaching time: 18 min.).Another batch of the same orange peels was subjected to the processdescribed in Example 7 of U.S. Pat. No. 3,982,003 (Mitchell) for thepreparation of food thickeners (i.e., adjusting the pH to 8.5 withsodium carbonate, enzymatic hydrolysis for 18 hours, and subsequentdewatering and drying).

The citrus absorbent material prepared according to the presentinvention (CAM) was compared with the starting material and with thematerial prepared according to the Mitchell patent (Mitchell) forchemical composition and absorbent properties.

    ______________________________________                                        A. GROSS CHEMICAL COMPOSITION                                                              Composition (% of dry weight)                                                   Whole Peel                                                     Component      Starting Material                                                                          CAM     Mitchell                                  ______________________________________                                        Pectin         25.6         47.4    32.7                                      Other polymers 20.4         48.1    30.8                                      Chloroform soluble lipids                                                                    5.96         0.87    3.91                                      Non-lipid organics                                                                           46.2         3.18    30.7                                      Water-soluble metal salts                                                                    1.80         0.43    1.85                                      ______________________________________                                        B. DISTRIBUTION OF PECTIN COMPONENTS                                                       Equivalent % of the                                                           polygalacturonic acid                                                           Whole Peel                                                     Component      Starting Material                                                                          CAM     Mitchell                                  ______________________________________                                        Methyl ester   59.5         7.2     14.1                                      Divalent metal salts                                                                         31.1         31.7    32.1                                      Monovalent metal salts                                                                       9.1          61.1    53.8                                      ______________________________________                                        C. CAPILLARY SORPTION CAPACITY                                                              Capacity, ml Synthetic Urine/g                                                Material, 1.0 psi                                               Test Conditions                                                                            CAM            Mitchell                                          ______________________________________                                        25 cm Absorb, 20 min                                                                       6.6            1.9                                               0 cm Void Volume, 30                                                                       8.2            4.4                                               min                                                                           25 cm Desorb, 20 min                                                                       7.1            2.5                                               ______________________________________                                        D. CAPILLARY SORPTION RATE                                                               25 cm Absorption                                                              Rate, ml Synthetic Urine/g Material/min.,                                     1.0 psi                                                            Measurement Time                                                                           CAM           Mitchell                                           ______________________________________                                        15 sec       1.9           0.1                                                30 sec       3.1           0.2                                                45 sec       4.1           0.3                                                1 min        5.2           0.3                                                2 min        6.1           0.6                                                10 min       6.5           1.5                                                ______________________________________                                    

The process described in the Mitchell patent, although it effectivelyreduces the degree of esterification of the pectin, fails to removeenough of the chloroform soluble lipids or of the non-lipid organics.The resulting material is only poorly absorbent. The material of thepresent invention possesses excellent absorbent properties.

Example Eight Calcium Hydroxide and Calcium Hypochlorite Treated OrangePeel Material

Florida Valencia oranges were juiced with an AMC Extractor and the peelswere machine shaved with a Brown Peel Shaver so that approximately 70%of the flavedo and 90% of the rag was removed. This material was groundin an Urschel grinder to a particle size of about 0.6 mm. Twenty fivepounds (about 11.3 kg) of the ground raw material at 12.4% solids, wasslurried in 60 pounds (27.24 kg) of water, making a 3.4% solids slurry.The slurry was titrated to pH 9.5 and maintained at this pH by causticaddition for 30 minutes. The titration tool 1.10 liters of 1N calciumhydroxide. The material was dewatered in a basket centrifuge. It waswashed with 75 pounds (about 34 kg) of water while spinning in thecentrifuge, and dewatered again. The 12.5 pounds (5.6 kg) of filter cakewas slurried in 65 pounds (29 kg) of water. 3.3 liters of 5.25% calciumhypochlorite bleach solution was added and the slurry was mixed for 18minutes. The bleached material was dewatered in the centrifuge. It waswashed again with 75 pounds (about 34 kg) of water while spinning andthen dewatered. This resulted in 10 pounds (4.45 kg) of material at14.06% solids.

The material was freeze dried to a moisture content of about 10%. Thematerial was essentially hydrophobic.

This example illustrates the detrimental effect of calcium ions on theabsorbent properties of the orange peel material.

Example Nine

Whole grapefruit peel was chopped into approximately 1/4 to 3/8 inch (ca6 mm×9 mm) cubes with a Fitzmill. The chopped peel was ground with anUrschel grinder. This ground peel was then chemically treated asfollows:

680 pounds (about 308 kg) of ground peel was slurried in 2500 pounds(about 770 kg) of soft water in a 500 gallon (about 1800 l) vessel understrong agitation. To this slurry was added a sufficient quantity of 1Normal sodium hydroxide to maintain the slurry pH between 9.0 and 9.5for at least 20 minutes. This required about 4 gallons (about 14liters). The slurry was then dewatered with a horizontal vacuum beltfilter to 7-12% solids.

The resulting filter cake was reslurried in 2500 pounds (about 770 kg)of soft water, again in a 500 gallon (about 1800 l) tank under strongagitation. To this slurry was added 0.10 pounds (about 45 g) of sodiumhypochlorite per pound of solids in the filter cake. The pH of theslurry was maintained at 9.0 to 11.0 by adding 1 Normal sodiumhydroxide. About 3 gallons (about 11 l) was used. The slurry wasmaintained in contact with the hypochlorite for about 45 minutes andthen dewatered again with a horizontal vacuum belt filter. Duringdewatering it was rinsed with 2500 to 5000 pounds (about 1135 kg toabout 2270 kg) of water.

The resulting filter cake was again slurried in 1600 pounds (about 726kg) of soft water in a 500 gallon (about 1800 l) tank under mildagitation. To this slurry was added 4 pounds (2.9 kg) of the nonionicsurfactant Tergitol 15-S-9 (Union Carbide), which is a secondary alcoholethoxylate. After 10 minutes of contact time, the slurry was once moredewatered with a horizontal vacuum belt filter, with no washing.

The resulting filter cake, containing 8.5% solids was flash dried in a12-inch (30 cm) Barr & Murphy ring flash dryer to produce a granularpowder, white to beige in color, containing 10% final moisture. Overallprocess yield from starting peel to final product was 45% on a solidsbasis.

    ______________________________________                                        PARTITION TEST                                                                Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Grapefruit Absorbent                                             Wood Pulp    Material                                                         ______________________________________                                        1.0          2.2                                                              2.0          5.0                                                              3.0          6.2                                                              4.0          7.0                                                              5.0          7.9                                                              ______________________________________                                    

These data demonstrate that the grapefruit absorbent material is highabsorbent.

Example Ten

Red Delicious apples were peeled, quartered, and cored and then the pulpwas processed in a disc shredder. One thousand grams of the shreddedapple pulp, at 15.36% solids, was slurried in a solution of 4000 mlwater and 25 ml 1N sodium hydroxide. The pH of the slurry, after addingthe apple pulp, was 10.50. After eleven minutes the pH dropped to 7.45;an additional 11 mis of 1N sodium hydroxide was slowly added, bringingthe slurry pH to 9.91. After a total time of thirty minutes, the slurrypH was 9.10. The material was dewatered in a basket centrifuge. It waswashed with 25 kg of water while spinning in the centrifuge, and thendewatered. One hundred ninety-five grams of material at 8.11% solid wascollected. One hundred and eighty-five grams of this material wasreslurried in a solution of 3800 ml of water and 200 ml of 5.25% sodiumhypochlorite solution, and mixed for eighteen minutes. The bleachedmaterial was dewatered in the centrifuge, then washed with 25 kg ofwater while spinning and then dewatered. The material was reslurriedwith 23 kg of water; then it was washed while spinning with 16 kg ofwater and dewatered. This resulted in 107.57 grams of material at 6.61%solids, yielding 4.63% of the initial shredded pulp solids. The materialwas freeze dried and its absorbent properties determined by thePartition Test.

    ______________________________________                                        PARTITION TEST                                                                Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Apple Absorbent                                                  Wood Pulp    Material                                                         ______________________________________                                        1.0          1.9                                                              2.0          4.1                                                              3.0          5.1                                                              4.0          7.5                                                              4.6          8.1                                                              ______________________________________                                    

These data demonstrate that the material is highly absorbent.

Example Eleven

Sugar beet shreds were processed into an absorbent material as follows:

The shreds were soaked for one hour in soft water, then washed, thenpassed through a Sprout-Waldron disc refiner at a 2% consistency. Afterrefining, the pH of the slurry was adjusted with sodium hydroxide toabout 9.8, and maintained at this value for about 30 minutes. The slurrywas then dewatered and washed with demineralized water, then slurried ina sodium hypochlorite solution (0.3 g Cl₂ per g solids at 2%consistency). The pH of the bleach solution was kept above 8.5 by addingsmall quantities of sodium hydroxide. The bleaching time was 54 minutes.After bleaching the pulp was washed with demineralized water, and passedthrough a Sprout-Waldron disc refiner. The material was washed fourtimes with isopropyl alcohol (isopropanol), then dried in a forced airoven at 70° C.

The resulting material had a fibrous appearance, with fiber dimensionssimilar to those of a conventional hardwood pulp. Its absorbentproperties were determined by the Partition Test.

    ______________________________________                                        PARTITION TEST                                                                Amount Absorbed, ml Synthetic Urine/g Material, 1.0 psi                       Reference    Sugar Beet Absorbent                                             Wood Pulp    Material                                                         ______________________________________                                        1.0          0.9                                                              2.0          3.1                                                              3.0          5.4                                                              4.0          7.2                                                              4.3          7.8                                                              ______________________________________                                    

The above process was modified in that the washings with isopropylalcohol were eliminated. Instead, the material was washed with softwater, then slurried at 2% consistency, in a 0.1% Tergitol solution, andflash dried. The resulting material was substantially similar to thematerial obtained after isopropyl alcohol treatment and oven-drying.

What is claimed is:
 1. An absorbent material derived from a vegetablematerial containing at least about 15% pectin, said absorbent materialcomprising:(a) from about 15% to about 60% pectin, said pectin having adegree of esterification of from about 1% to about 45%, and from 18.5%to about 50% of the pectin being in the form of a divalent metal salt;(b) from about 15% to about 80% of a material selected from the groupconsisting of cellulose, hemicellulose, lignin and mixtures thereof; (c)from 0% to about 1% chloroform soluble lipids; (d) from 0% to about 10%non-lipid organic materials extractable in a mixture of chloroform,methanol and water, said mixture having a volume ratiochloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.
 2. A vegetable-derived absorbent materialaccording to claim 1 wherein less than about 30% of the pectin is in theform of a calcium salt.
 3. A vegetable-derived absorbent materialaccording to claim 1 wherein the pectin has a degree of esterificationof less than about 20%.
 4. A vegetable-derived absorbent materialaccording to claim 1 which is prepared from citrus peels, sugar beetpulp, apples, or mixtures thereof.
 5. A citrus peel-derived absorbentmaterial comprising:(a) from about 30% to about 60% pectin, said pectinhaving a degree of esterification of less than about 20%, and from 29.8%to about 30% of the pectin being in the form of a calcium salt; (b) fromabout 30% to about 60% of a mixture of cellulose and hemicellulose; (c)from 0% to about 1% chloroform soluble lipids; (d) from 0% to about 105non-lipid organic materials extractable in a mixture of chloroform,methanol and water, said mixture having a volume ratiochloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.
 6. A sugar beet-derived absorbent materialcomprising:(a) from about 15% to about 35% pectin, said pectin having adegree of esterification of less than about 45%, and from 18.4% to about30% of the pectin being in the form of a calcium salt; (b) from about20% to about 80% of a mixture of cellulose and hemicellulose; (c) from0% to about 1% chloroform soluble lipids; (d) from 0% to about 10%non-lipid organic materials extractable in a mixture of chloroform,methanol and water, said mixture having a volume ratiochloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.
 7. An absorbent material derived from avegetable material containing at least about 15% pectin, said absorbentmaterial comprising:(a) from about 15% to about 60% pectin, said pectinhaving a degree of esterification of from about 1% to about 45%, andless than about 50% of the pectin being in the form of a divalent metalsalt, wherein the amount of divalent metal salt in the absorbentmaterial is about the same as the amount naturally present in thevegetable material; (b) from about 15% to about 80% of a materialselected from the group consisting of cellulose, hemicellulose, ligninand mixtures thereof; (c) from 0% to about 1% chloroform soluble lipids;(d) from 0% to about 10% non-lipid organic materials extractable in amixture of chloroform, methanol and water, said mixture having a volumeratio chloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.
 8. A citrus peel-derived absorbent materialcomprising:(a) from about 30% to about 60% pectin, said pectin having adegree of esterification of less than about 20%, and less than about 30%of the pectin being in the form of a calcium salt, wherein the amount ofcalcium salt in the absorbent material is about the same as the amountnaturally present in the citrus peel; (b) from about 30% to about 60% ofa mixture of cellulose and hemicellulose; (c) from 0% to about 1%chloroform soluble lipids; (d) from 0% to about 10% non-lipid organicmaterials extractable in a mixture of chloroform, methanol and water,said mixture having a volume ratio chloroform:methanol:water of 20:4:1;and (e) from 0% to about 6% water-soluble metal salts.
 9. A sugarbeet-derived absorbent material comprising:(a) from about 15% to about35% pectin, said pectin having a degree of esterification of less thanabout 45%, and less than about 30% of the pectin being in the form of acalcium salt, wherein the amount of calcium salt in the absorbentmaterial is about the same as the amount naturally present in the sugarbeet; (b) from about 20% to about 80% of a mixture of cellulose andhemicellulose; (c) from 0% to about 1% chloroform soluble lipids; (d)from 0% to about 10% non-lipid organic materials extractable in amixture of chloroform, methanol and water, said mixture having a volumeratio chloroform:methanol:water of 20:4:1; and (e) from 0% to about 6%water-soluble metal salts.